Method and suction dredging installation for obtaining sand

ABSTRACT

In dredging sand, an inner pipe is movable longitudinally within an outer jacket so that the lower end of the inner pipe may be projected beyond the lower end of the jacket and retracted within the jacket. Suction is maintained on the inner pipe and water under pressure is supplied to the jacket so that, when retracted, the lower end of the inner pipe draws in a mixture of sand and water entering the lower end of the jacket to provide the desired suspension in the pipe. In intermediate positions, the lower end portion of the inner pipe blocks the lower end of the jacket but the lower end portion of the inner pipe is formed to communicate the lower end of the inner pipe with the water under pressure in the jacket.

United States Patent [72] Inventor Jan De Koning Amsterdam, Netherlands [21 Appl. No. 765,420 [22] Filed Oct. 7, 1968 [45] Patented June 22, 1971 [73] Assignee N. V. lngenieursburean voor Systemen en Octrooien Spanstaal Rotterdam, Netherlands [32] Priority Oct. 16, 1967 [33] Netherlands [31] 67.14009 [54] METHOD AND SUCTION DREDGING INSTALLATION FOR OBTAINING SAND 6 Claims, 5 Drawing Figs.

[52] US. Cl 1. 37/58, 37/57, 37/195, 302/58, 302/15,175/403 [51] int. Cl E02! 3/88, E02f 3/92, 1502i 3/94 [50] FieldofSearch 37/57, 58, 61-63, 195;302/14, 15, 58,64, 66; 299/8; 175/5, 6, 20, 403, 405

[56] References Cited UNYTED STATES PATENTS 1,861,349 5/1932 Lockett ..I 37/61 X 336,619 2/1886 Badger 37/58 1,758,047 5/1930 Jensen 37/62 2,774,569 12/1956 Jacobsen.. 37/63 3,153,290 10/1964 Saito 37/62 3,163,241 12/1964 Daigle et a1 175/405 X FORElGN PATENTS 837,669 6/ 1960 Great Britain 37/58 6,501,404 8/1966 Netherlands 37/58 6,501,405 8/1966 Netherlands 37/58 6,604,227 10/1967 Netherlands 37/58 Primary Examiner-Robert E. Pulfrey Assistant Examiner-Clifford D. Crowder Attorney-Imirie, Smiley, Snyder and Butrum T ABSTRACT: In dredging sand, an inner pipe is movable 1ongitudinally within an outer jacket so that the lower end of the inner pipe may be projected beyond the lower end of the jacket and retracted within the jacket. Suction is maintained on the inner pipe and water under pressure is supplied to the jacket so that, when retracted, the lower end of the inner pipe draws in a mixture of sand andwater entering the lower end of the jacket to provide the desired suspension in the pipe. In intermediate positions, the lower end portion of the inner pipe blocks the lower end of the jacket but the lower end portion of the inner pipe is formed to communicate the lower end of the inner pipe with the water under pressure in the jacket.

PATENTED JUNE 212m SHEET 1 BF 2 INVENTOR JAN n: mwiwe ATTORNIzYS METHOD AND SUCTION DREDGING INSTALLATION FOR OBTAINING SAND The invention relates to a method for obtaining sand with the aid of a suction-dredging installation having a pump disposed between a suction pipe and a discharge pipe, the suction pipe being inserted a relatively considerable distance into the soil. The invention also relates to a suction-dredging installation for obtaining dredging spoil for instance sand, comprising a suction pipe having an inner pipe, a sliding pipe disposed at the lower end of the inner pipe and telescopically cooperating therewith, ajacket enclosing the inner pipe and the sliding pipe, and drive means for driving the sliding pipe, the sliding pipe having at its lower end at least one suction mouth for sucking up dredging spoil.

The invention relates more particularly to the obtaining of sand which lies below a layer ofa different kind of soil, such as clay or loam. When the sand is below a layer of clay, the suction pipe must first penetrate the clay layer before the sand can be sucked up. The penetration of the suction pipe through the clay layer is difficult and requires a considerable amount of unproductive time. It is the first object of the present invention to reduce this unproductive time to a small fraction of the total operating time. This is obtained in that during an interruption of the suction process the suction pipe is left in the sand. In this way the number of unproductive periods, and therefore the total unproductive or less productive time are considerably reduced. The interruption of the suction process can be related to, for instance, rest periods for the operatives performing this method, or maintenance work on the pump or other components of the suction-dredging installation.

If in the conventional method the discharge of sand at the delivery side must be terminated, for instance, because the barges which receive and transport the sand have not arrived in time at the suction-dredging installation, the suction pipe is removed from the bed of sand, which removal subsequently causes an unproductive period on the resumption of the suction process. In contrast, if a shorter stoppage is expected, for instance, of one-half or 1 hour, the suction process is usually continued and the sand sucked up is thrown overboard and thus is lost. The present invention obviates this loss of sand since it permits the suction pipe to be left in the sand while the suction is terminated.

Generally it is feared that the suction pipe will get stuck in the bed. In the method according to the invention the suction pipe will irretrievably get stuck in the bed. The invention is based on the realization that a firmly fixed suction pipe is no hindrance, since it can suck itself loose. To this end a hollow of increasing periphery is produced adjacent the lower end of the suction pipe on resumption of the suction process. The sand present above the hollow is then fluidized, since it is not sufficiently supported at the lower side.

This hollow can be produced in principle by known means, such as spout nozzles or cutting tools acting on the sand in front of the suction mouth of the suction pipe. To make the suction process fully productive very quickly, for instance within five minutes after an interruption, the invention also improves a suction-dredging installation for obtaining dredging spoil, for instance sand, comprising a suction pipe having a inner pipe a sliding pipe disposed at the lower end of the inner pipe and telescopically cooperating therewith, a jacket enclosing the inner pipe and the sliding pipe, and drive means for driving the sliding pipe, the sliding pipe having at its lower end at least one suction mouth for sucking up dredging spoil by the fact that the lower end of the telescopic pipe can be extended free outside the jacket fixed firmly in the bed and can be again retracted into the jacket.

The suction process can be reliably resumed after an interruption if during the interruption of the suction process water under pressure is supplied to the lower end of the suction pipe, while the suction effect of the pump is gradually eliminated at the lower end of the suction pipe.

The last-mentioned suction-dredging installation according to the invention has been further developed by the adoption of inexpensive features, so that it operates more efficiently during the penetration of the clay layer by the suction pipe, the normal suction process, and the resumption thereof after an interruption. 7

These and other features of the invention will be illucidated in the following description with reference to the accompanying diagrammatic drawings, wherein:

FIG. 1 is a cutaway side elevation of the lower member of the suction pipe in a preferred embodiment of a suctiondredging installation according to the invention;

FIGS. 2 and 3 show situations during the penetration of the pipe through a clay layer;

FIG. 4 shows a situation during the cleaning of the grid; and

FIG. 5 shows a situation during the release of the firmly fixed suction pipe.

FIG. 1 shows only the lower member of a suction pipe 33 which is pivotably connected in know manner to a top member of the suction pipe pivotably suspended from a suction-dredging installation loading into barges. The bottom member of the suction pipe 33 mainly consists of an inner pipe 34 which is connected via the top member to a sand pump disposed, for instance, 10 m. below the level of the water; a jacket 35 which encloses the inner pipe 34 and is rigidly connected thereto; and a long sliding pipe 37 which is mounted axially slidably in the inner pipe 34 which is driven axially by means of'a number, for instance three, of hydraulic cylinders 36 and which has at its lower end a pipe portion 42 of larger diameter. This pipe portion 42 carries a strainer 38 which forms the grid for keeping out large objects, such as rocks, which may be in the soil, and which has front grid 44 extending transversely of the suction pipe 33 and an adjoining cylindrical grid 41. The outer diameter of the cylindrical grid 41 corresponds with the internal diameter of the somewhat narrowed jacket end 39 of the jacket 35, so that during he withdrawal of the sliding pipe 37 into the jacket end 39, the lower edge 40 of the jacket end 39 scrapes off the cylindrical grid 41 any large objects which may have stuck thereto. Internally, the cylindrical grid 41 is connected to the lower end of the pipe portion 42 which is of the same diameter as the cylindrical grid 41 and is lengthened at its end remote from the cylindrical grid 41 by a guide pipe 43 of the same diameter. The guide pipe 43 and therefore the pipe portion 42 is connected by radial butt straps 53 to a reduced diameter portion 54 of the sliding pipe 37. The portion 54 is provided at its lower end with a radial collar 55 which presents an annular gap 52 between the collar 55 and the pipe portion 42. The guide pipe 43 has a sliding fit in the jacket end 39. The lower end portion 54 of the sliding pipe 37 and the guide pipe 43, define a cylindrical space 45 therebetween which is in communication at its top end with the interior 46 of the jacket 35, the space 46 being connected to a supply 47 of water under pressure obtained from a pump delivering water under regulatable pressure. The water under pressure can emerge from the space 46 through the gap 52 into the pipe portion 42.

The jacket 35 has a jacket portion 48 of larger cross section, for receiving the cylinders 36. To keep the suction pipe 33 as slender as possible at its lower end, the inner pipe 34 is relatively short and the sliding pipe 37 is specially long, for instance 20 m. in length, while the travel of the sliding pipe 37 is only 4 m.

Guide bridges 49 are provided to guide the long sliding pipe 37 in relation to the jacket 35.

For the purpose of making a hole in the sand or the like, the jacket end 39 of the suction pipe 33 has a sharp lower edge 40, while as a result of the wide pipe portion 42 at the end of the sliding pipe 37, and the annular gap 52 for the admission of water under pressure, the resistance is low when flow enters into the sliding pipe 37 as explained in copending application Ser. No. 765,421, filed Oct. 7, 1968.

This is a consequency of a toroidal supporting vortex 60 caused by the inflowing water under pressure. It is true that flow conditions are not as satisfactory adjacent the lower edge 40, but this is no hindrance, at that point the flow cross section is relatively large.

While the suction pipe 33 is inserted into the hard clay layer 50 (cf. FIG. 2), the supply 47 of water under pressure is cut off, the sliding pipe 37 with the strainer 38 is kept retracted, and the jacket end 39 is forced into the clay, while a large amount of water is sucked in by the sand pump as illustrated by the arrows 18 in FIG. 2. In this stage a large amount of clay 51 penetrates the lower end of the suction pipe 33. Arrows 18 in FIGS. 2 and 3 show how the water flows down along the outside of the jacket end 39, bends around the lower edge 40, and finally flow between the portion of clay 51 and the inner wall of the jacket end 39 up into the strainer 38. Since the lower edge 40 is continuously caused to follow the bottom 25 the eroded cylindrical cavity, the width of gap at the location of the lower edge 40 and the bottom 25 is very small, and therefore the local velocity of the water flow is very high, so that the water flow rapidly erodes the soil of the firm bed below the lower edge 40. Moreover, the large portion of clay 51 is eroded at its side, so that its diameter becomes smaller than the internal diameter of the jacket end 39 A downward pressure is then exerted by means of the strainer 38 to upset the portion ofclay 51 (cf. FIG. 3).

The speed of flow between the upset portion of clay 51 and the jacket end 39 then becomes greater, so that the erosion on the outer surface of the large portion of clay 51 increases. Moreover, the coherence of the portion of clay 51 is considerably reduced during its upsetting. Preferably, the lower edge 40 is continuously introduced more deeply into the soil, so that the speed of flow around the lower edge 40 remains high. Further, the portion of clay 51 which has entered the jacket end is upset continuously, or with short interruptions. In this way the time taken for inserting the suction pipe into the soil thus the unproductive time can be shortened considerably.

When the jacket end 39 is in the sand below the clay layer 50, the position of the strainer 38 in the jacket end 39 is regulated in dependence on the column of soil which is disposed in the space above the lower edge 40, and in dependence on the pressure of the water supplied to the pipe portion 42 via the gap 52. The concentration of sand in the suspension sucked up can therefore be regulated.

When too many large objects have become accumulated below the strainer 38 in the jacket end 39, the strainer 38 is driven outwards, so that sand can enter through the cylindrical grid 41 (cf. FIG. 4). Owing thereto the suctional pressure on the front grid 44 is considerably reduced, and large objects can drop off the front grid 44, also as a result of movements of the suction pipe.

in the unlikely event of the suction pipe 33 getting stuck in compacted sand 57 enclosing the jacket 35, for instance after the sudden collapse of an unexpectedly high wall of sand or by unskilled maneuvering, the sliding pipe 37 is continuously moved up and down against the compacted sand disposed below the suction pipe 33, while a large quantity of water under pressure is supplied through the gap 52 and sucked in by the sand pump. The sliding pipe 37 with the strainer 38 thus attacks the compacted sand beneath the suction pipe 33. On each reciprocation, the telescopic pipe 37 can be extended slightly further, until it has reached its maximum extended position. With the length of stroke of the cylinders 36 equal to 4 m., the strainer can travel, for instance, 2 m. outwards and 2 m. inwards.

When the sliding pipe 37 with strainer 38 is retracted, a hollow 56 is formed in the still compacted sand 57 below the suction pipe. Any sand present above the hollow 56 which is supported neither by the fixed jacket 35 nor the strainer 38, drops down into the hollow and is sucked in with the next outward stroke of the sliding pipe 37. The resulting larger hollow 58 therefore progressively increases in size, until all the sand 57 shown within the chain line 59 adjacent the suction pipe 33 is fluidized. The suction pipe 33 can then again be moved as required.

Summarizing the above it may be stated that owing to the movable sliding pipe 37 the suction pipe 33 is specially suitable for penetrating quickly through a compacted clay layer; for sucking up a suspension with an adjusted high concentration of sand; for obtaining sand at a site where large rocks occur; and for automatically releasing itself, when it has become stuck.

So as to have to make the suction pipe penetrate the clay layer less often, when the suction process is interrupted, the suction pipe is not taken out of the soil, but left therein, so that when the suction process is resumed, the suction pipe has only to be sucked loose, for instance, in the manner described hereinbefore. This method is adopted not only when the suction process has been interrupted for a rest period or for the performance of necessary maintenance work, but also if the supply of sand is obstructed. This step prevents a large amount of sand from being lost by being thrown on to the clay layer, where it becomes partly mixed with the mud floating on the clay layer and partly penetrates into the disturbed clay layer.

During the stoppage of the suction process, water is forced through the annular gap 52 into the pipe portion 42 of the sliding pipe 37, and the suctional effect at the lower end of the sliding pipe 37 is eliminated by admitting water through a valve in a higher portion of the suction pipe 33 valve communicates with the outer water. Water is therefore mainly led up from the gap 52 through the sliding pipe 37, while the sand is retained below the gap 52. It is therefore impossible for sand to get stuck in the part of the suction pipe disposed above the gap 52. It is true that sand gets stuck around the jacket 35, in the lower end of the jacket and in the lower end of the sliding pipe, but this sand can readily be fluidized on resumption of the suction process.

lclaim: l. A method of sucking up a suspension of sand in water comprising the following successive steps of:

progressively inserting the free and unobstructed lower extremity of ajacket into a body of sand under water,

withdrawing a suspension of sand in water from within said jacket by sucking at the top end of a suction pipe whose lower end is within said jacket and is spaced upwardly above the lower extremity thereof while simultaneously introducing water into said jacket at a pressure sufficient to commingle water and sand at said lower end of the suction pipe to form said suspension, and continuing such withdrawal of suspension during a first withdrawal period until the lower extremity of the jacket is at a substantial depth at which the sand ordinarily may not be fluidized solely by suction to recreate the suspension once the suction is terminated,

interrupting the withdrawal operation during an interruption period while the lower extremity of the jacket is at said substantial depth,

fluidizing the sand in the region of said lower extremity of the jacket by reciprocating the lower end of said suction pipe outwardly through said lower extremity of the jacket into contact with the body of sand and back into the jacket while sucking on the suction pipe and introducing water into the jacket as aforesaid so as to establish an environment which is mainly water at said region,

and then withdrawing suspension through said suction pipe from within said jacket during a second withdrawal period,

wherein the end of the jacket is maintained in the ground during the first withdrawal period, the interruption period and the second withdrawal period.

2. A suction-dredging installation for sucking up dredging spoil, comprising a suction pipe having an inner pipe, means for selectively maintaining suction on said inner pipe, a sliding pipe disposed at the lower end of the inner pipe and telescopically cooperating therewith, a jacket enclosing the inner pipe and the sliding pipe and having a lower extremity which is free and unobstructed, the sliding pipe having at its lower end at least one suction mouth for sucking up dredging spoil, means for introducing water into said jacket under sufficient pressure to commingle water with sand at said suction mouth to form a suspension of sand in water thereat which is withdrawn through said sliding pipe and said inner pipe due. to said suction, and drive means for driving the sliding pipe to move between a position in which its lower end is retracted within said jacket and a position in which it is projected through said lower extremity of the jacket into contact with a body of sand surrounding saidjacket. I 1 3. Suction dredging apparatus comprising, in combination;

an elongate tubular jacket having a lower end portion of predetermined cross section and a second portion immediately above said lower end portion which is of greater cross section than said predetermined cross section, said jacket having a lower extremity which is completely free and unobstructed and is adapted to be inserted into an underwater body of sand whereby a column of sand tends to rise in said jacket due to the static head of sand above said lower extremity;

suction pipe means within said jacket and having a lower end portion dimensioned to fit closely but slidably within said lower end portion of said jacket, said lower end portion of the suction pipe means comprising a sliding pipe having a lower extremity adapted to induct a suspension of sand in water and guide pipe mans at least partially surrounding the lower extremity of said sliding pipe for communicating the lower extremity of said sliding pipe with said second portion of the jacket;

means for longitudinally shifting said suction pipe mans relative to said jacket between one extreme position in which the lower end portion of said suction pipe means projects through the lower end portion of said jacket portion of the jacket in the space between said sliding pipe and the jacket under sufficient pressure to reach said lower extremity of said sliding pipe whereby the suction on said sliding pipe commingles such water with sand at the lower extremity of said sliding pipe and forms said suspension in said sliding pipe.

4. The suction dredging apparatus as defined in claim 3 including valve means for admitting water into said inner pipe at a level well above the lower extremity thereof to eliminate suction on said inner pipe.

5. The suction-dredging apparatus as defined in claim 4 wherein said guide pipe means is formed by a sleeve surrounding and radially spaced from the lower extremity of said inner pipe, said sleeve extending above and below, said lower extremity and being rigid therewith.

6 The suction-dredging apparatus as defined in claim 3 wherein said guide pipe means is formed by a sleeve surrounding and radially spaced from the lower extremity of said inner pipe, said sleeve extending above and below said lower extremity and being rigid therewith. 

1. A method of sucking up a suspension of sand in water comprising the following successive steps of: progressively inserting the free and unobstructed lower extremity of a jacket into a body of sand under water, withdrawing a suspension of sand in water from within said jacket by sucking at the top end of a suction pipe whose lower end is within said jacket and is spaced upwardly above the lower extremity thereof while simultaneously introducing water into said jacket at a pressure sufficient to commingle water and sand at said lower end of the suction pipe to form said suspension, and continuing such withdrawal of suspension during a first withdrawal period until the lower extremity of the jacket is at a substantial depth at which the sand ordinarily may not be fluidized solely by suction to recreate the suspension once the suction is terminated, interrupting the withdrawal operation during an interruption period while the lower extremity of the jacket is at said substantial depth, fluidizing the sand in the region of said lower extremity of the jacket by reciprocating the lower end of said suction pipe outwardly through said lower extremity of the jacket into contact with the body of sand and back into the jacket while sucking on the suction pipe and introducing water into the jacket as aforesaid so as to establish an environment which is mainly water at said region, and then withdrawing suspension through said suction pipe from within said jacket during a second withdrawal period, wherein the end of the jacket is maintained in the ground during the first withdrawal period, the interruption period and the second withdrawal period.
 2. A suction-dredging installation for sucking up dredging spoil, comprising a suction pipe having an inner pipe, means for selectively maintaining suction on said inner pipe, a sliding pipe disposed at the lower end of the inner pipe and telescopically cooperating therewith, a jacket enclosing the inner pipe and the sliding pipe and having a lower extremity which is free and unobstructed, the sliding pipe having at its lower end at least one suction mouth for sucking up dredging spoil, means for introducing water into said jacket under sufficient pressure to commingle water with sand at said suction mouth to form a suspension of sand in water thereat which is withdrawn through said sliding pipe and said inner pipe due to said suction, and drive means for driving the sliding pipe to move between a position in which its lower end is retracted within said jacket and a position in which it is projected through said lower extremity of the jacket into contact with a body of sand surrounding said jacket.
 3. Suction dredging apparatus comprising, in combination; an elongate tubular jacket having a lower end portion of predetermined cross section and a second portion immediately above said lower end portion which is of greater cross section than said predetermined cross section, said jacket having a lower extremity which is completely free and unobstructed and is adapted to be inserted into an underwater body of sand whereby a column of sand tends to rise in said jacket due to the static head of sand above said lower extremity; suction pipe means within said jacket and having a lower end portion dimensioned to fit closely but slidably within said lower end portion of said jacket, said lower end portion of the suction pipe means comprising a sliding pipe having a lower extremity adapted to induct a suspension of sand in water and guide pipe mans at least partially surrounding the lower extremity of said sliding pipe for communicating the lower extremity of said sliding pipe with said second portion of the jacket; means for longitudinally shifting said suction pipe mans relAtive to said jacket between one extreme position in which the lower end portion of said suction pipe means projects through the lower end portion of said jacket whereby the lower end portion of the suction pipe means may contact an underwater body of sand into which said jacket is inserted, and a further extreme position in which said lower end portion of the suction pipe means is retracted within said jacket; means for selectively maintaining suction on said sliding pipe to withdraw a suspension of sand in water therethrough; means for supplying water into the interior of said second portion of the jacket in the space between said sliding pipe and the jacket under sufficient pressure to reach said lower extremity of said sliding pipe whereby the suction on said sliding pipe commingles such water with sand at the lower extremity of said sliding pipe and forms said suspension in said sliding pipe.
 4. The suction dredging apparatus as defined in claim 3 including valve means for admitting water into said inner pipe at a level well above the lower extremity thereof to eliminate suction on said inner pipe.
 5. The suction-dredging apparatus as defined in claim 4 wherein said guide pipe means is formed by a sleeve surrounding and radially spaced from the lower extremity of said inner pipe, said sleeve extending above and below said lower extremity and being rigid therewith. 6 The suction-dredging apparatus as defined in claim 3 wherein said guide pipe means is formed by a sleeve surrounding and radially spaced from the lower extremity of said inner pipe, said sleeve extending above and below said lower extremity and being rigid therewith. 